Outside groups are driving the spending on broadcast television ads in the final months of the Michigan Senate race and Democrats are dominating the spending battle, according to a breakdown compiled by Republican firm Echelon Insights for Terri Lynn Land's campaign.

Land is running against Democratic Rep. Gary Peters in the open seat contest.

In the past month, 54.89 percent of ad spending in the race has come from outside groups, a higher percentage than any other Senate race in the country, according to the data, provided to CQ Roll Call.

Alaska is the only other state where more than half of ad spending comes from outside groups. Iowa and Colorado also have a high percentage of outside spending.

The bulk of that spending came from Democratic groups, with NextGen Climate, a group funded by billionaire Tom Steyer that focuses on environmental issues, at the top.

Democrats have far outspent Republicans here over the past month. Sixty-one percent of the spots aired on broadcast television over the past month were from Democrats, while Republicans funded 39 percent.

Spending from Democrats has ramped up dramatically over the past two weeks, particularly from the Democratic Senatorial Campaign Committee.

(Courtesy Echelon Insights)

Senate Majority PAC also has played in the race. On the Republican side, Ending Spending PAC has been one of the most active outside groups, along with the NRSC.

Echelon Insights projects Democrats will continue to dominate spending in this race, with an estimate they will air 73 percent of spots over the next week and 76 percent of ads over the next three weeks. Of course, those reservations for air time could always be changed.

Echelon Insights based the data on 11,190 spots and the $6.2 million spent to air them.

Peters has an edge in this race for the seat currently held by retiring Democratic Sen. Carl Levin, and he has led in all polls. But recent surveys have shown the race starting to tighten in Land's direction. Republicans need to gain six seats to take control of the Senate next year.

For now, Democrats are favored to hold this one. The Rothenberg Political Report/Roll Call rates this race Leans Democratic .